Modulating system



Feb. 8, 1949. J. J. ANTALEK uoDULATING SYSTEM 2 sheets-sheet 1 Filed Nov. 13, 1944 A TOR 0R [VENTO Feb. 8, 1949. J. J. ANTALEK MODULATING SYSTEM 2 Sheets-'sheet 2 Filed Nov. 15,. 1944 INVENTOR ,fo/n .IAvaZer ATTORNEY Patented Feb. s, 1949 MODULATING SYSTEM John J. Antaiek, Chicago, Ill., assignor to The Bauland Corporation, Chicago, Ill., a corporation of Illinois Application November 13, 1944, Serial No. 563,275v v Claims. (C1. 332-30) This invention` relates to modulating systems and, in particular, to circuits the capacitive characteristics of which are varied in accordance with an input signal and the output of which is used to modulate another circuit in accordance with the input signals. I'he modulating system comprises one or more condensers the capacity of which is varied by a direct current applied to the terminals of the condenser or condensers.

I have found, particularly when using condensers of high dielectric constant, especially those exceeding a dieletcric constant of 75, that the application of D. C. voltage to its terminals changes its capacity in a predetermined manner which depends on the capacity and the voltage ranges used. The relationship -between capacity and D. C. voltage may be of any type, preferably linear, and it can be adjustable within any predetermined range by changing capacities and D. C. voltages accordingly. This relationship, however, need not necessarily be linear, depending on the use made of the capacity variations.

Such capacity variations, for example, may be applied to control the frequency characteristic of an electric circuit and, in particular, its resonance or anti-resonance characteristics. In such a case, the capacity variationsmay be used to de- The capacity variations may further be used p to control an automatic volume control to vary in accordance with a control voltage derived, for example, in a communication system, from the output of an audio frequency stage of the circuit. These capacity variations maybe used to modulate the amplitude or the frequency in an. intermediate radio frequency stage of the communis cation system.

The characteristic of the capacity-D. C. voltage response, therefore, will depend substantially upon the effect to be desired. Very often, a nonlinear capacity-voltage response will be required at the outset. and this response will be compensated by a corresponding frequency response of non-linear but inverse characteristic and the resulting modulating eect can be made linear.

On the other hand, when a non-linear modulating effect is required, the capacity-D. C. voltage response will have to be arranged in such a way that, taking into account intermediate energy transfers, the final modulating eifect would have the desired non-linear characteristic. All

this can be accomplished without exceeding the scope of this invention. y

A specific modulating circuit, according to this invention, contains two condensers of high dielectric constant in series. One terminal of a. source of D. C. voltage is applied to the series connection of the two condensers while the other terminal of the D. C. voltage source is applied to the remaining terminal of one of the condensers. The output is taken from those terminals of the two condensers which are not connected with each other.

The terminals of the condensers which are connected in series should preferably, but not necessarily, be placed on the positive pole of the D. C. voltage source while its negative pole is connected to the remaining terminal of one of the condensers.

The input of the modulating circuit'may contain a radio frequency isolating resistor. This is particularly useful in the case of controlling the frequency of an oscillator.

In -case of modulating the amplitude or the frequency of a carrier wave, the input circuit may contain an inductance, for instance,- one winding of a transformer which, through a second winding, in inductlvely -coupled with an oscillating circuit, the frequency or amplitude of which is to be modulated in accordance with this inven- A Fig. 3 shows a circuit according to this invenl tion controlling an automaticvolume control system;

Fig. 4 shows a frequency modulation employing the invention;

Fig. 5 showsl a preferred form of a condenser circuit l of high dielectric constant. such as can be used in a circuit according to this invention;

Fig. 6 shows another form of condenser of high` the voltage-capacity characteristic in such a. condenser.

In Fig. 1, condensers I and 2 have a high dielectric constant and are connected in series. Their common terminals are connected through 'resistor `3 to one pole I, preferably the positive pole, ofa` D. C. input voltage. The two outer terminals of condenser-s I and 2 are connected in series with an inductance 5, one of which of these terminals is connected to the negative pole B of the D. C. input voltage, or to ground. l K The condensers I and 2 are preferably of equal size and have the same characteristics. I have found only dielectric media belonging to the titanium family group and of qualities which are now commercially available to have a dielectric constant greater than 75 useful for the purpose of this invention, for example, titanium dioxide,

titanium dioxide magnesium titanate, titanium dioxide titanium-zirconium dioxide.

'A dielectric of this type includes, apart from a titanium composition, a ceramic binder coated with silver. Such a condenser is shown in more detail in Fig. 5 where 23 represents the dielectric medium and 2l and 25 the silvei` electrodes of the condenser.

Condensers I and 2 are high dielectric constant ceramic condensers of the following characteristics: They tune load inductance 5. When a D. C. voltage is applied to the D. C. input terminals l and 5, the capacity of both condensers I and 2 is reduced, resulting in a higher resonant frequency for the anti-resonant circuit I; 2, 5.

In this way, the resonant frequency of the circuit I, 2, 5 may be varied directly with the D. C. input voltage applied across condensers I and 2. Circuit I, 2, 5 is used to control the operating frequency (or operating frequency band) of an oscillator (or radio frequency amplifier) tube 1.

Fig. 2 shows a similar but modified circuit wherein the output of an A. C. voltage source, such as a microphone 9 in series with battery I0, may be impressed upon the modulating circuit I, 2, 5 by 4superimposing it upon an appropriate direct potential impressed across terminals 4, 6.

A. C. voltage may be used to vary the capacity, providing it is combined with a D. C. voltage equal to or greater than the peak-to-peak A. C. voltage. If the A. C. voltage to be applied is thus combined .vith a direct potential of adequate magnitude they will add togetheralgebraically to produce a resulting voltage of unchanging polarity but varying magnitude and the capacity will vary in accordance with the variations of magnitude, i. e. in accordance with the A. C. signal component. In the present application the terms D. C. potential" or "direct potential are intended to include varying voltages which do not change inpolarity, i. e. voltages includinga steady D. C. component and an A. C. component or ripple never larger in its peak-to-peak value than the D. C. component.

Part II is a radio-frequency choke used to isolate the radio-frequency circuit from the audiofrequency circuit. A resistor may be used instead of this choke. Transformer I2 serves to couple A. C. source 9-I Il to the modulating circuit I, 2, 5. The D. C. input voltage applied to terminals 4, 5 must be high enough so that the peak-to-peak A. C. voltage could never exceed its value. Circuit I, 2, 5 is connected to an oscillator or radio-frequency amplifier I3 to frequency modulate the energy generated in or passing through it.

Such a circuit is especially adaptable to the frequency modulation of an oscillator or as a variable impedance device at any fixed frequency.

A circuit such as shown in Fig. 1 may be used as an automatic means for controlling volume where circuit I, 2, 5 is used as a resonant coupling means in a radio frequency or intermediate frequency amplifier. The D. C. voltage 4, 6 may be afforded by the voltage developed across a diode detector load in a receiver.

This is explained in more detail in Fig. 3 where an intermediate frequency is controlled. Circuit I, 2,y 5 represents aV modulating circuit according. to this invention, while circuits I4 and I5 represent the input and output circuits of an intermediate frequency stage, each containing variable Condensers I5, 'I'I and inductances i8, I9. The automaticvolume control voltage is applied over terminals 4, 5 and resistance 20 to the common connection terminals of condensers I, 2 and to the remaining free terminal of condenser 2, respectively.

Fig. 4 shows a frequency modulation system employing the circuit as illustrated in Fig. 2.

The output of modulating circuit I, 2, E is fed to a tetrode 2I and therefrom through trans-V former 22 into the output circuit. Transformer I2 may be preceded, if desired. by -an amplifier tube (not shown) to increase the band width of the frequency modulated carrier.

Fig. 5 shows a cross section through a preferred form of a condenser of high dielectric constant having a dielectric compound 23 and electrodes 2l, 25 which may consist of metal plates or of coatings composed of silver or any other conducting material. 25 and 21 are connecting leads.

Fig. 6 shows a, modified condenser inwhich the high dielectric constant material 23 is positioned between pointed electrodes 28, 29 to which connecting leads 30, II are attached.

Fig. l illustrates schematically the control circuit employed according to this invention. The condenser as illustrated in Fig. 6 is arranged at 32 in series with a condenser 33 of .01 micro-farad capacity which is not affected by the D. C. control voltage.

With a particular sample of dielectric material in a condenser as shown in Fig. 5, the following voltage-capacity characteristics were obtained:

Table 1 xp ned Vofage Capacity Mfd.

o .0034 so .oom mo .com iso .0034s zoo .com aso .costas aoo .ooaiss Table 2 A lied Vlg me capacity Mld. o .0034 10o .0034s coo .costi aoo .ocaso The retrace characteristic of the Condensers was found to be satisfactory. However, condensers employing the same type of construction may not always have the same voltage-capacity characteristics as shown in the above tables.

Table 3 Appued fr e Voltage Capmfy Mmfd'. 2.3 1w 2.1 200 1.9 l 300 1.5 I 4m 1.15

What I claim'is:

H-output inductance in series with Qsaid condesers,

a choke in series between said source and said one of the condensers for preventing passage of radio frequency energy rfrom said'circuit through saidk source, an input inductance arranged also in series between. said source and said one of the lio condensers, and an input circuit inductively coupled with said input inductance.

4. In an automatic volume control system. an anti-resonant link circuit comprising at least two condensers connected in series, at least one of vsaid condensers havingla dielectric with a constant exceeding 75 and a capacity which varies when different direct potentialsvareeapplied across it, a source of direct control potentials connected across said one of said condensers,

. and an inductance in series with each cl2 said 1. In a modulating system a resonant circuit comprising at least one condenser with an amorphous dielectric having a constant exceeding 75, means for` applying diilerent direct potentials across said condenser for varying its capacity to vary the frequency at which the circuit is resonant, said condenser having pointed electrodes impinging on opposite sides of saiddielectric and said circuit including in series with said one condenser a second condenser with a dielectric which is of different composition and lower dielectric constant.

2. In a frequency modulating system, a circuit comprising at least two condensers connected in series, at least one of said condensers having an amorphous dielectric with a. constant exceeding 75 and a capacity which varies when different 'direct potentials are applied across it, a source of modulating direct potentials connected across said one of said condensers and comprising a direct current source for providing a xed direct potential, a signal source for providing varying signal potentials and a circuit forcombining the direct potential and the signal potentials, an output inductance connected in series with said condensers, and a resistor in series with said source of modulatingl potentials and said one oi the condensers.

3. In a modulating system, a circuit comprising at least two ,condensers connected in lseries,`at least one of said condensers havinga dielectric with a constant exceeding 75 and a capacity which varies when dinerent direct potentials are applied across it, a source or direct potentials applied across said one of said condensers. an

Number condensers and across both of them, a resistor in series between said source and said one of said condensers, an anti-resonant intermediate frequency input circuit comprising an inductive element inductively coupled with said inductance and an Vanti-resonant intermediate output cire cuit also comprising an inductive element inductively coupled with said inductance.

5. A system according to claim 3, and including means for varying the inductance of said output inductance to control the operating range oi the modulation system. *l

JOHN J. AN'I'AIEK.

REFERENCES CITED l The following references are of record in the ille of this patent:

UNIITED STATES PATENTS Name Date 1,684,680 Hentschel Oct. 24, 1932 2,032,620 Langmuir Mar. 3, 1936 2,054,431 Lindenblad Sept. 15, 1936 2,071,564 Nicolson Feb. 23, 1937 l 2,121,737 Hansell June 21, 1938 2,141,292 Clavier Dec. 27, 1938 2,182,377 Guanella Dec. 5, 1939 2,191,315 Guanella Feb.. 20, 1940 2,243,921 Rust et al. June 3, 1941 2,306,555 Mueller Dec. 29, 1942 2,368,643 CrosbyA Feb. 6, 1945 2,402,518 Wainer June 18, 1946 1 ed., 1943, published by McGraw-Hill Book Company, page 111. (Copy in Division 51.) 

